Intel IXP2800 8.2.1 Receive Pins, 8.2.2 RBUF

248 Hardware Reference Manual
Intel® IXP2800 Network Processor
Media and Switch Fabric Interface
8.2.1 Receive Pins
The use of the receive pins is a function of RPROT input, as shown in Table 8 6.
In general, hardware does framing, parity checking, and flow control message handling.
Interpretation of frame header and payload data is done by Microengine software.
The internal clock used is taken from the RCLK pin. RCLK_Ref output is a buffered version of
the clock. It can be used to supply TCLK_Ref of the Egress IXP2800 Network Processor if
desired.
The receive pins RDAT[15:0], RCTL, RPAR are sampled relative to RCLK. To work at high
frequencies, each of those pins has de-skewing logic as described in Section8 .6.
8.2.2 RBUF
RBUF is a RAM that holds received data. It stores received data in sub-blocks (referred to as
elements), and is accessed by a Microengine or the Intel XScale® core reading the received
information. Details of how RBUF elements are allocated and filled is based on the receive data
protocol, and is described in Section 8.2.2.1 – Section 8.2.2.2. When data is received, the
associated status is put into the Full_Element_List FIFO and subsequently sent to a Microengine
for processing. Full_Element_List insures that received elements are sent to a Microengine in the
order in which the data was received.
RBUF contains a total of eight Kbytes of data. Table 8 7 shows the order in which received data is
stored in RBUF. Each number represents a byte, in order of arrival from the receiver interface.
The mapping of elements to address offset in RBUF is based on the RBUF partition and element
size, as programmed in the MSF_Rx_Control CSR. RBUF can be partitioned into one, two, or
three partitions based on MSF_Rx_Control[RBUF_Partition]. The mapping of received data to
partitions is shown in Table88.
Table 86. Receive Pins Usage by Protocol
Name Direction SPI-4 Use CSIX Use
RCLK Input RDCLK TxClk
RDAT[15:0] Input RDAT[15:0] TxData[15:0]
RCTL Input RCTL TxSOF
RPAR Input Not Used TxPar
RSCLK Output RSCLK Not Used
RSTAT[1:0] Output RSTAT[1:0] Not Used
Table 87. Order in which Received Data Is Stored in RBUF
Data/Payload Address Offset (Hex)
45670123 0
CDEF8 9 A B 8
14 15 16 17 10 11 12 13 10